A zipper is widely utilized in our modern life which is a device for temporarily combining two flexible materials and is primarily applied to cloth, leather or other textile products. According to the structural difference, zippers can be divided into two types: coil form and individual form. The coil zipper is advantageous for convenient manufacturing procedure, low cost and easily being processed, so that it is widely used in ready-made clothes. The coil zipper is formed by twisting polyester filaments, and thus, it is also called a polyester zipper. Also, in the past the zipper is always formed by nylon, so that it is also called a nylon zipper. The common coil zipper, as shown in FIG. 1 and FIG. 2, includes two different coils 3, 3a which are sewn on different base cloths 2, 2a by stitches 1, and the coils 3, 3a respectively have plural chain teeth 4. Between the coils 3, 3a, a slider 5 is mounted, and through a back and forth movement of the slider 5, the chain teeth 4 on the coils 3, 3a will be combined or separated, so as to temporarily combine or separate the two base cloths 2, 2a. The slider 5 has a track 6 for penetrating the coils 3, 3a, and since the common coils 3, 3a may respectively have a slightly protruded curve 7 at the top thereof, when the slider 5 slides back and forth, the tops of the coils 3, 3a might collide with the track 6 owing to an excessive forcing or an incorrect forcing direction. Further, because the coil zipper is formed by polyester filament, which is not as tough as the metal material, it might be easily destroyed by an excessive collision. Besides, the stitches 1 are also wound around the tops of the coils 3, 3a, so that when the slider 5 is sliding, the stitches 1 might rub against the inner side of the track 6 and carelessly pull and drag the coils 3, 3a, and thus, after a long term using, the stitches might be broken or come off, or the coils 3, 3a might be deformed, such that the connection between the coils 3, 3a and the base cloths 2, 2a will be influenced.
In the conventional patents of R.O.C. patents No. M262054 and No. M263797, the improved structures of the nylon zipper are disclosed, in which the top surfaces of the two chain teeth, or both the top and the bottom surfaces of the two chain teeth are formed to have a stitch indentation for positioning the stitches, and since the stitches are limited by the stitch indentation, the situations that the stitches wind around the chain teeth, come off and rub against the slider can be prevented. However, because the surface of the chain teeth is small, the addition of the stitch indentation might reduce the strength of the zipper structure, so that it actually is difficult to install the stitch indentation and the cost might also be increased thereby. Consequently, the technology of the two conventional patents also can not effectively solve the deformation problem of chain teeth which is caused by the slider colliding with or pulling and dragging the chain teeth as sliding.